Spine has two main meanings that connect in an interesting way.

Your spine is the column of bones running down the center of your back, from your skull to your hips. Also called the backbone or spinal column, it's made up of small bones called vertebrae stacked on top of each other like blocks. Your spine protects the spinal cord, a thick bundle of nerves that carries messages between your brain and the rest of your body. It also holds you upright and lets you bend, twist, and move. Without a spine, you'd collapse like a rag doll. Animals with spines, including humans, fish, birds, and reptiles, are called vertebrates.

The word also means courage and strength of character. When someone shows spine, they stand up for what they believe is right even when it's difficult or unpopular. A student who defends a classmate being teased shows spine. A scientist who challenges incorrect ideas despite criticism from others demonstrates spine.

The word can also refer to the bound edge of a book where the pages attach, which you see when books sit on a shelf.